We have reported in this paper the complete cDNA sequence, gene structure, and tissue-specific expression of LOXL2, a new amine oxidase and a member of an emerging family of human lysyl oxidases. The predicted amino acid sequence, from several overlapping cDNA clones isolated from placenta and spleen cDNA libraries, shared extensive sequence homology with the conserved copper-binding and catalytic domains of both lysyl oxidase (LOX) and the lysyl oxidase-like (LOXL) protein. These conserved domains are encoded by five consecutive exons within the LOX, LOXL, and LOXL2 genes that also maintained exon-intron structure conservation. In contrast, six exons encoding the aminoterminal domains diverged both in sequence and structure. Exon 1 of the LOXL2 gene does not encode a signal sequence that is present in LOX and LOXL, suggesting a different processing and intracellular localization for this new protein. Expression of the LOXL2 gene was detected in almost all tissues with the highest steady state mRNA levels in the reproductive tissues, placenta, uterus and prostate. In situ hybridization identified placental syncytial and cytotrophoblasts responsible for the synthesis of LOXL2 mRNA and demonstrated a spatial and temporal expression pattern unique to the LOXL2 gene.Lysyl oxidase is a copper-dependent amine oxidase that belongs to a heterogeneous family of enzymes that oxidize primary amine substrates to reactive aldehydes. This enzyme family is subdivided into two main classes on the basis of the chemical nature of the co-factors associated with these amine oxidases. Flavine adenine dinucleotide is the co-factor of monoamine oxidase and of an intracellular form of polyamine oxidase. A second group of amine oxidases contain topaquinone, a modified tyrosine side chain utilized as a redox co-factor. Diamine oxidase, monoamine-metabolizing semi-carbazide-sensitive amine oxidase, and lysyl oxidase belong to this latter subfamily of amine oxidases (1-3).Most of the studies on lysyl oxidase have focused on the specific cross-linking activity and catalytic mechanism of action of this enzyme on the extracellular matrix substrates, collagen and elastin. Lysyl oxidase participates in the critical post-translational modification essential to the biogenesis of connective tissue by deaminating the side chains of lysine residues in these proteins, thus catalyzing the covalent crosslinking of several fibrillar collagen types and the formation of desmosine and isodesmosine cross-links in elastin (4, 5).Recently, multiple novel biological functions have been attributed to lysyl oxidase (6, 7) that have suggested that other intracellular and intranuclear substrates may be involved in these multiple functions (8, 9). The range of these novel activities of lysyl oxidase cover a spectrum of biological functions from developmental regulation (10) to tumor suppression (7,(11)(12)(13)(14) and cell growth control (15, 16). An attractive hypothesis to explain how a single protein can fulfill these different functions is that a family of seve...

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The decidua and placenta synthesize the human relaxins, termed H1 and H2, believed to be involved in collagen remodeling in the amnion and chorion in an autocrine/paracrine manner. The developmental regulation of the relaxin genes was quantitated in normal pregnancy by in situ hybridization histochemistry with six 48-mer oligonucleotide probes that detect both relaxin genes. A significant increase in relaxin expression occurred in both decidua (p < 0.01) and placenta (p < 0.05) at 12.5-14.4 wk gestation, with the mean peak value in the placenta more than double that of the decidua, suggesting a coordinate regulation of the relaxin genes. At term after spontaneous labor and delivery, a marginal increase in both decidual and placental relaxin gene expression occurred. Given these normal data, three abnormal preterm situations were investigated: 1) premature uterine contractions without prior rupture of the membranes, 2) premature rupture of the fetal membranes (PPROM), 3) cesarean section for medical reasons with intact membranes and no uterine contractions. Tissues showing intrauterine infection were eliminated. Significantly more relaxin was expressed in the preterm decidua from patients with PPROM when compared to patients in group 1 (p < 0.02) or group 3 (p < 0.008). These data were confirmed by Northern analysis with a relaxin cRNA probe. The placental tissues after PPROM also had a significantly higher and a uniform overexpression of relaxin in the placental syncytiotrophoblast. Tissues collected at term, in comparison, showed no such increases in decidua or placenta.

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